GARDENS Jane PowersAutumn's zingy reds and purples are some of nature's better tricks
At the time of writing, autumn has been a bit of a damp squib, but perhaps by the time you're reading this it will have crisped up a little. Cold nights and sunny days are what is needed for that most heartening of seasonal phenomena: autumn colour.
Swapping cool green foliage for a clatter of fiery golden, orange, and crimson leaves is one of nature's better tricks. As the growing season nears its end, chlorophyll, the green pigment, fades from the tissues of deciduous leaves. Its job, as one of the players in the photosynthesis process, is finished for the year. When it melts away it unmasks the underlying colour of the leaf - often a warm yellow - just as a ripening banana turns from green to yellow. These golden hues, called carotenoids, are revealed only by the leaking away of the green.
The season's zingy reds and purples - the anthocyanins - are produced by sugars trapped in the leaves. Warm, sunny days make more sugars form; cold nights cause the leaf veins to close up, capturing the sugars. So a soggy autumn, such as the one enfolding the trees as I type, is not conducive to igniting fireworks in their foliage.
The katsura tree (Cercidiphyllum japonicum), which is one of the first to turn (and lose) its leaves, from early October onwards, has put on a modest show this year, with its faded-yellow leaves just barely flushed with pink. Nonetheless, it has an unexpected stunt up its sleeve, no matter what the autumn weather. Its drying leaves exude a sweet, burnt-sugar smell, so that you catch a barely perceptible whiff of candy floss when you pass by. This east Asian native's sugary gifts to the nose make it one of my favourites in the autumn garden.
If you're looking for resounding, eye-popping autumn leaf colour, then the very best tree is the sweet gum, from the eastern United States. We know it here by its botanical name, Liquidambar, from the Latin for liquid and amber. It is so called because some species exude a fragrant resin, storax, that - believe it or not - led to the invention of polystyrene. There are Asian liquidambars, but it is the American one, L styraciflua, that has the ritziest colour. Its foliage makes a brilliant and long-lasting patchwork of orange, red and deep maroon, often remaining intact until well into December. But it is a commodious tree, so don't think of planting it unless you can accommodate its eventual 20m height and 10m width.
Liquidambar is easily confused with maple, as it has similar-looking palmate leaves, but the two are not related. It is, in fact, a member of the witch-hazel family (which enjoys the mouth-filling name of Hamamelidaceae), a clan that includes several autumn show-offs. The witch hazels themselves (Hamamelis) mostly turn a pleasing yellow, but some, including the copper-flowered 'Diane', become a blaze of gold, orange and red. Other flamboyant relatives are the slow-growing and spreading Persian ironwood (Parrotia persica), the heart-leaved Disanthus cercidifolius, from Japan and southeast China, and the bottle-brush-flowered Fothergilla species from the southeastern United States. Both Disanthus and Fothergilla require an acid
soil.
But back to maples - the real ones, that is. The genus Acer contains some of the flashiest autumn trees in the world, namely the New England forest maples. Red maple, sugar maple and silver maple (A rubrum, A saccharum and A saccharinum) are the main providers of fall colour in the northeastern states of America. But, being great big strapping forest trees, they are too large for the domestic garden here - unless you have a spare field or two.
For garden-sized acers we must look to Asia and the hundreds of Japanese maples, which range in size from weeny specimens barely a metre tall to small trees of up to eight metres. All have exquisitely decorative leaves, which turn yellow (at least) and orange and crimson (at best) when chilly weather hits. Acer palmatum 'Osakazuki' is one of the showiest - and most widely available - with green leaves turning to a vibrant crimson. It can reach six metres in height when mature, but it grows at a slow and contemplative pace.
Japanese maples need shelter and a moist and humus-laden soil (just think of decades of leaf mould cushioning a forest floor and you get the idea). Nonetheless, the smaller ones may be grown in pots for years. Use a soil-based compost (such as John Innes No 3), replacing the top couple of centimetres yearly, and adding a handful of pelleted poultry manure.
If you keep it watered in the summer and treat it nicely, even a diminutive maple in a pot will ensure that the season goes out with a neat little bang instead of a dull whimper.
AUTUMN TREES AND SHRUBS
Amelanchier (June berry or snowy mespilus) Large shrub or small tree. Leaves turn yellow, orange and red.
Berberis thunbergii (barberry) Good red autumn colour and bright berries.
Betula (birch): buttery yellow in autumn.
Cornus (dogwood) Trees and shrubs with good autumn colour (especially C kousa and cultivars of C florida and C alba) in yellow, dark orange and maroon.
Cotinus coggygria (smoke bush) Large shrub with blue-green or purple, smooth leaves; orange, red or crimson in autumn.
Euonymus (spindle tree) The native E europaeus and the Asian E alatus and E planipes all have red autumn foliage.
Enkianthus campanulatus Large (to four metres) Japanese shrub with bell-shaped flowers and multicoloured autumn foliage; needs lime-free soil.
Larix (larch) Deciduous conifers that turn gold before dropping their needles.
Liriodendron tulipifera (tulip tree) Very large tree with curious cut-off leaves and big, sparsely borne, tulip-like flowers; yellow autumn foliage.
Nyssa sylvatica (tupelo) Slow-growing, medium-sized tree with ovate leaves that turn yellow, orange and red; lime-free soil.
Prunus (cherry) Many cherries have yellow or orangey autumn colour; our native wild cherry (P avium) and the Japanese P sargentii turn orange and scarlet.
Rhododendron luteum (azalea) Orange, crimson and purple foliage in autumn; lime-free soil.
Rhus typhina (stag's horn sumach) Small, elegant tree; orange and crimson leaves.
Our native mountain ash (S aucuparia) has yellow to orange autumn foliage; other fiery-leaved members of the genus are S commixta, S serotina and 'Joseph Rock'.
Our native guelder rose (V opulus) and V plicatum, from China and Japan, have orange to wine autumn leaves.
AUTUMN CLIMBERS
All have radiant, red autumn colour, including Virginia creeper (P quinquefolia) and Boston ivy (P tricuspidata).
Vitis (vine) Most Vitis species have yellow or red autumn leaves; the purple-leaved ornamental grape (V vinifera 'Purpurea') turns dark maroon; the enormous, hairy leaves of V coignetiae go bright red.